Piles suitable for subsidence conditions

ABSTRACT

A TELESCOPIC PILE SUITABLE FOR SUPPORTING A FOUNDATION ON SOILS UNDERGOING CONSOLIDATION PROCESSES AND IN GENERAL FOR SUBSIDENCE CONDITIONS, COMPRISING A SOLID ELONGATED LOWER MEMBER, VERTICALLY ARRANGED AND BEARING ON A FIRM STRATUM, AND A HOLLOW ELONGATED MEMBER TELESCOPICALLY MOUNTED OVER THE TOP OF SAID SOLID MEMBER AND CONTAINING A FILL OF GRAVEL OR OTHER GRANULAR MATERIAL BEARING ON TOP OF SAID SOLID MEMBER AND EXERTING A POSITIVE INNER FRICTION ON THE INNER WALLS OF SAID HOLLOW MEMBER, THE TOP OF SAID HOLLOW MEMBER BEING ARRANGED TO SUPPORT A FOUNDATION BUILT ON THE SURFACE OF THE SOIL. THE BEARING CAPACITY OF THE ABOVE DESCRIBED PILE IS DERIVED FROM POSITIVE SKIN FRICTION AS WELL AS FROM POINT RESISTANCE. THE FORMER IS DEVELOPED THROUGH FRICTION BETWEEN THE UPPER HOLLOW SECTION OF THE PILE AND THE SURROUNDING SOIL AND THE LATTER IS DUE TO THE REACTION OF THE   FIRM STRATUM ON THE LOWER TIP OF THE SOLID MEMBER OF THE PILE. THE LOAD IS TRANSMITTED TO THE TIP THROUGH FRICTION BETWEEN THE UPPER HOLLOW SECTION AND THE GRAVEL OR SAID FILL.

Jan. 19, 1971 .J. J. CORREA PILES SUITABLE FOR SUBSIDENCE CONDITIONS Filed Aug. 1, 19769 United States Patent O 3,555,833 PILES SUITABLE FOR SUBSIDENCE CONDITIONS Juan J. Correa, Av. Lindavista 229,

Mexico City, Mexico Filed Aug. 1, 1969, Ser. No. 846,7 71 Int. Cl. E02d 5 /52 U.S. Cl. 61-53 6 'Claims ABSTRACT F THE DISCLOSURE A telescopic pile suitable for supporting a foundation on soils undergoing consolidation processes and in general for subsidence conditions, comprising a solid elongated lower member, vertically arranged and bearing on a firm stratum, and a hollow elongated member telescopically mounted over the top of said solid member and containing a f`1ll of gravel or other granular material bearing on top of said solid member and exerting a positive inner friction on the inner walls of said hollow member, the top of said hollow member being arranged to support a foundation built on the surface of the soil.

The bearing capacity of the above described pile is derived from positive skin friction as well as from point resistance. The former is developed through friction between the upper hollow section of the pile and the surrounding soil and the latter is due to the reaction of the firm stratum on the lower tip of the solid member of the pile. The load is transmitted to the tip through friction between the upper hollow section and the gravel or said ll.

BACKGROUND OF THE INVENTION The present invention refers to the building art and, more particularly, it is related to improvements in piles highly useful for subsidence conditions of the soil on which the foundation supported by the pile is built, said pile deriving its bearing capacity from a positive skin friction action'and a point resistance, and being of a telescopic type in order to allow the foundation to settle concomitantly with the settling speed of the soil surrounding it.

In places where subsidence conditions in the soil exist, foundation of heavy buildings has become a serious problem, therefore several solutions have been proposed and used for many years. The various proposed solutions, however, have not been very efficient or they have been rather costly.

Among the several solutions proposed, the following can be mentioned: Control piles, compensated friction pile foundations and negative friction piles. However, the application of the above mentioned solutions to support the foundations of several buildings have produced results which leave much to desire, therefore for long it has been the aim of those who are skillful in the building art, to nd a type of pile which, while being very economical and of simple construction, will nevertheless provide for the compensation of the relative position of a foundation with respect to the soil surface when subsidence conditions of the soil surrounding the pile exist.

In other words, when heavy buildings are erected on soft soil in which subsidence conditions exist, it is well known that, in order to achieve a rm foundation, it becomes necessary to drive piles vertically through the soil until a firm stratum is reached, in order that the foundation may be solidly supported on said rm stratum. How- Patented Jan. 19, 1971 ever, when subsidence conditions exist, the soil settles down, for instance, through a decrease in its volume due to water pumping from wells, and therefore said soil tends to hang from the piles, thus increasing its load and furthermore producing the visible effect that the building supported thereon apparently emerges from the soil, with the consequent problems created thereby, such as damages to neighboring houses and public utilities.

With the aim of solving the above problem, it has been customary to drive into the soil friction piles which are not driven down to a firm stratum but, on the contrary, the points thereof are left approximately l0 feet or more above said firm stratum, so that, when the soil surface slowly goes down, the foundations supported by the piles will also concurrently settle down. However, friction piles of this type sometimes produce settlements of the foundations which are supported thereon on the occasion of earth movements such as those produced by earthquakes and the like. Moreover, the loading capacity of these friction piles depends only on the positive friction exerted on the outer surface of the piles in contact with the surrounding soil, thus very large loads cannot be supported thereby.

Control piles are also very widely used in order to solve the problems created by subsidence conditions in the soil, but said control piles are nothing but point bearing piles driven down to bear on a rm stratum and connected to the foundation on the heads thereof, through a device which can be deformed at will and in accordance with the speed of settlement of the surrounding soil, so that the building can be maintained at the same level as the said surrounding soil.

While the above types of piles of the prior art were effective to avoid the problem of emergence of buildings supported on soil wherein subsidence conditions exist, it will be obvious to those skilled in the art that compensated friction pile foundations require deep excavations for heavy buildings, while control piles have very expensive devices which furtherly need to be periodically maintained, with the concomitant high cost of construction and maintenance.

SUMMARY OF THE INVENTION Having in mind the defects of the prior art piles, it is an object of the present invention to provide a telescopic type of pile which will be highly suitable to control the settlement of buildings built on soils wherein subsidence conditions exist.

Another object of the present invention is to provide an improved pile of the above character in which the bearing capacity is derived from combined positive skin friction and point resistance under said subsoil conditions.

It is a further object of the present invention to provide an improved telescopic pile of the type described, wherein the controlling action of the pile is automatically exerted by the mere provision of a hollow telescopic member wherein a granular ll is provided to create a positive friction on the inner walls thereof.

It is a further object of the present invention to provide an improved telescopic pile of the above mentioned character, having a higher bearing capacity and a lower settlement when used in conjunction with a compensated foundation, or needing a more shallow depth of foundation for equal settlements.

The foregoing objects and others ancillary thereto are preferably accomplished as follows:

According to a preferred embodiment of the present invention, a solid elongated pile member, preferably a cylindrical pile member, is driven through the soft soil until the lower tip thereof bears on a rm geological formation. A hollow elongated pile member, preferably a tubular pile member is driven through said soil such that it is telescopically arranged in respect of said cylindrical member, and a granular ll is provided within the hollow tubular member, said iill being of a height duly calculated to exert a positive friction on the inner walls of the tubular member, such that the bearing capacity of the pile be derived from positive skin friction between the upper hollow section and the surrounding soil, and from point resistance exerted by bearing of the point of said solid member on a firm soil or rock. The load is transmitted to the tip through friction between the upper hollow section and the gravel or said lill.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features that are considered characteristic of the present invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment thereof, when read in connection with the accompanying drawings, in which:

FIG. l is a perspective view of the telescopic pile built in accordance with a preferred embodiment of the invention; and

FIG. 2 is a longitudinal cross sectional view of the pile of FIG. l, showing the different elements comprising it and their relative position with respect to the supported foundation and the firm geological formation.

DETAILED DESCRIPTION Having now more particular reference to the drawings, the telescopic pile of the present invention generally comprises a lower solid elongated member 1, which in the illustrative embodiment shown in the drawing is a cylindrical member but which can adopt any other shape, driven through the surrounding soil 8 until the lower point 12 thereof bears on a rm soil or rock 3, and a tubular hollow member 2 having a cavity 4, which is driven through the soil 8 such that its lower end 13 will be overlapped t the upper end or head 10 of member 1 as more clearly illustrated in FIG. 2 of the drawings. The upper end on head 11 of the tubular member 2 supports the foundation which is located approximately at the level 7 of the ground.

The outer diameter of member 1 and the inner diameter of member 2 are such that enough clearance 14 is left between both members, so as to allow a slipping motion therebetween.

A till of granular material 5 is provided within cavity 4 of member 2, at a height or upper level 9 carefully computed so as to produce a skin friction on the inner wall of member 2, suitable for supporting the load of the structure 6 and the building supported thereby.

The above described pile built in accordance with the present invention, works as follows:

The load produced by the structure 6 applied at the head 11 of member 2, is partially transmitted to the surrounding soil 8 through skin friction as diagrammatically indicated by the upwardly pointing arrows 15, and the remainder is carried on by the lower section 1 which supports on its head 10 the fill 5, said till developing a predetermined friction, diagrammatically indicated by the upwardly pointing arrows 16, against the inner surface of the tubular upper member 2. Finally, the lower member 1 bears through its point 12, on a firm stratum 3 with a working stress which can be computed with a suitable safety factor to duly support the building.

The upper level 9 of the gravel ll 5 within cavity 4 of the upper member 2 is generally determined on the basis that the friction exerted against the inner surface of said tubular member will reach an ultimate value and the downward movement of the upper member 2 is effected at the same velocity as the surface of the surround ing soil 8. If the movement of this member 2 were slower, due to an underestimate of said ultimate friction, a negative friction would develop that would force down the upper member 2, thus increasing the values of the inner friction 16, until the ultimate value is reached. If the ultimate friction 16 were overestimated and if the pile foundation above described is combined with a raft, such as is a usual practice in soil undergoing settlements, that is, where subsidence conditions exist, the net vertical pressures transmitted to the soil through the raft, would be increased and actual settlements of the foundation with respect to the surrounding soil surface would be larger than those commited by considering the upper member 2 as a friction pile. Therefore, it can be concluded that it is preferable to design the ll 5 such that the upper level thereof will be selected to provide an inner friction value which is under the ultimate value.

The fill 5 contained within cavity 4 of member 2 can be selected from gravel, sand, scrap iron, slag and any other granular material, preferably a low-priced material.

As to the pile members 1 and 2, said members can be made of any suitable material selected from those used in pile construction, such as plain concrete, reinforced concrete, pre-stressed concrete, post-compressed concrete, steel, wood or any combination of said materials.

ADVANTAGES OF THE INVENTION The above described telescopic type of pile ishighly suitable for subsoils undergoing consolidation processes, provided that a firm soil or rock can be economically reached by the pile tips.

-Due to the telescopic action of the upper pile member upon the lower pile member, most of the negative friction is avoided, thus providing more useful load conditions than those usually assigned to point bearing piles.

On the other hand, the foundation can follow the movement of the adjacent soil surface, provided that the gravel fill is properly designed and constructed, thus avoiding damages to neighboring buildings founded on shallow foundations.

This type of pile can be used with advantage in conjunction with a partially compensated raft foundation, and under these conditions the telescopic piles provide better results than friction piles, inasmuch as the settlements are smaller if the depth of the foundation raft is the same, or the foundation level can be higher for equal settlements.

Finally, the piles of the present invention also possess a higher load capacity than friction piles, due to the inner friction developed by the till of granular material.

Although a preferred specific embodiment of the present invention has been lshown and described in the above, many modifications thereof are possible. The invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

That which is claimed as new, is:

1. A telescopic pile suitable for supporting foundations on a soil where subsidence conditions exist, comprising a solid elongated member which is driven into the soil until the lower point thereof bears on firm soil or rock, a hollow elongated member telescopically inserted on top of said solid elongated member and supporting a foundation on the upper head thereof, said head forming the bottom of the cavity in said hollow elongated member, and a iill of granular material bearing on the head of said solid elongated member and contained within the cavity of said hollow elongated member, in order to exert a positive friction on the inner Wall thereof.

2. A telescopic pile according to claim 1 wherein said granular material is gravel.

3. A telescopic pile according to claim 1 wherein said granular material is sand.

y4. A telescopic pile according to claim 1 wherein said granular material is scrap iron.

5 5. A telescopic pile according to claim 1 wherein said granular material is slag.

6. A telescopic pile according to claim 1 wherein said solid elongated member is an elongated cylindrical member having ilat ends, the lower of which bears on firm soil 5 References Cited UNITED STATES PATENTS JACOB SHAPIRO, Primary Examiner 

